1) Field of the Invention
This invention relates to a method for characterizing powder samples by calculating the energy level of and forces produced on a powder within a rotating sample container and how the powder reacts to these forces. The information produced by these measurements can determine how well a powder performs in various processes and equipment such as pharmaceutical tableting machines, pneumatics conveyors, container filling machines, drying systems, and catalyst towers.
2) Description of the Related Art
Many systems have been disclosed and produced that measure powder properties in rotating cylindrical containers. These systems use various sensing techniques to measure powder behavior including photo-arrays, torque sensors, load cells, and video cameras. All of these systems consist of placing powder in a cylindrical sample container and then rotating the container about its lengthwise axis. The behavior of the powder due to the rotation of the sample container is then measured.
A system for characterizing powder avalanche in a rotating drum is disclosed by B. H. Kaye in Powder and Bulk Engineering, February, 1996. In the disclosed system, a light beam is directed through a transparent, rotating drum containing a powder sample. As the drum rotates, the powder avalanches at periodic intervals. A photocell array positioned on the opposite side of the drum is blocked to a greater or lesser degree as the powder avalanches within the drum. The output of the photocell array represents powder avalanching within the drum. This system only provides information as to the time between avalanches and does not calculate the energy level of the powder or forces acting on the powder or the energy released by each avalanche.
Another system for characterizing powder avalanches is disclosed in U.S. Pat. No. 5,847,294. In the disclosed system, a torque sensor is used to sense avalanches as the sample drum is rotated. The torque sensor measures the moment produced by the powder as it moves from the center of the drum to a position that is off center. When the powder avalanches, it moves back toward the center of the drum, reducing the moment and thus the torque on the torque sensor. This system provides information as to the time between avalanches and an indicator of avalanche size but does not calculate the energy level of the powder or forces acting on the powder or the energy released by each avalanche.
Another system for characterizing powder avalanches is disclosed in U.S. Pat. No. 5,959,222. In the disclosed system, an energy beam scanner is mounted inside the rotating sample drum to detect movement of the sample powder. The output of the energy beam scanner represents powder avalanching within the drum. This system only provides information as to the time between avalanches and does not calculate the energy level of the powder or forces acting on the powder or the energy released by each avalanche.
Another system for characterizing powder is disclosed by Alexander, Chaudhuri, Faqih, Muzzio Davies, Tomassone, in Powder Technology, January 2006. In the disclosed system, a load cell is used to sense powder position as the sample drum is rotated. The load cell measures the moment produced by the powder as it moves from the center of the drum to a position that is off center. When the powder avalanches, it moves back toward the center of the drum reducing the moment and thus the load on the torque sensor. This has the same weakness as the system disclosed in U.S. Pat. No. 5,847,294.
Another system for characterizing powder in a rotating drum is disclosed by M A S Quintanilla, J M Valverde, A Castellanos in the Journal of Statistical Mechanics, July 2006. In the disclosed system, a video camera is used to measure powder properties as the sample drum is rotated. In this system, angle of the powder is extracted from the images of the powder. Avalanches are detected by change in angle of the powder. This system does not calculate the energy level of the powder or forces acting on the powder or the energy released by each avalanche.
A commercial system for characterizing powder in a rotating drum is disclosed by Mercury Scientific Inc. In the disclosed system, a video camera is used to measure powder properties as the sample drum is rotated. In this system, angle of the powder and height of the powder in the sample drum is extracted from the images of the powder. The height of the powder is multiplied by the volume of the powder to produce a power value for the powder as it moves in the drum. Avalanches are detected by a change in the power of the powder. This system does not calculate the energy level of the powder or forces acting on the powder or the energy released by each avalanche. Also, powder angles are generally not reliably calculated because powders in rotating drums produce curved surfaces which have no defined angle.
None of the disclosed systems calculate or estimate the actual potential energy level of the powder as it is repositioned by the rotation of the sample container. They also do not calculate the amount of energy required to produce an avalanche in the powder or the amount of energy loss produced by an avalanche. They also do not measure the dependence of the potential energy, avalanche size, or energy required to produce an avalanche on the rotation speed of the container. Nor do they measure the curvature of the powder surface or the dependence of the curvature on rotation speed.